Method and composition for the prevention or retarding of staling and its effect during the baking process of bakery products

ABSTRACT

The present invention is related to a method for the prevention or retarding of staling during the baking process of bakery products which comprises the step of adding a sufficiently effective amount of at least one intermediate thermostable and/or thermostable serine protease in said bakery products. The present invention further relates to an improver composition for the prevention or retarding of staling during the baking process of bakery products, characterised in that it comprises at least one intermediate thermostable and/or thermostable serine protease.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/510,401, filed May 12, 2005, which is the 371 National StageApplication based on International PCT Application NumberPCT/BE03/00062, filed Apr. 7, 2003, which claims priority to EuropeanPatent Application No. 02447056.9, filed Apr. 5, 2002, the contents ofwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention concerns a method and a composition for theprevention or retarding of staling and associated effects during thebaking process of bakery products which comprise at least oneintermediate thermostable and/or thermostable serine protease.

BACKGROUND OF THE INVENTION

The consumers prefer to buy fresh bread and they want it to remain freshfor a long time. Retarding the staling has always been a challenge toproducers of bakery ingredients. The fact that the production of breadis more and more centralised and farther away from the distributionpoints puts an even larger pressure on the development of additives andingredients to maintain the softness of bread. Also soft rolls,hamburger, buns and pastry products are subject to staling and a loss ofsoftness. There are a number of ingredients known to retard the stalingof bread and soft bakery products. Fat and emulsifiers such as distilledmonoglycerides and stearoyllactylates are already used since decades.Mono-, di- and polysaccharides have a positive influence on waterretention and binding. Water loss is often associated with staling andthe saccharides have positive influence on the mouthfeel of bakedproducts and thus diminish the perception of staling. Amylases are knownto have a beneficial effect on staling and starch retrogradation.

Bread staling is a complex phenomenon. It is perceived as a softening ofthe crust, a hardening of the crumb and the disappearance of fresh breadflavour. The hardening of the crumb is not only due to a loss of waterduring storage as was already demonstrated by Boussingault in ((1852)Ann. Chim. Phys. 3,36,490). It is the result of a number ofphysico-chemical processes. Over the years, researchers have tried tounravel these processes and developed different theories.

In the early days, bread firming was attributed solely to theretrogradation of starch (Katz, J. R. (1930) Z. Phys. Chem., 150,37-59). It was shown by X-ray diffraction that the starch in bread isforming a micro-crystalline structure during storage. Later it was shownthat the water soluble starch fraction diminished during bread staling(Schoch et al. (1947) Cereal Chem., 24, 231-249), which concludes thatduring baking starch granules absorb water. The linear amylose chainsbecome soluble and diffuse to the water phase. In time more and moreamylose is present in the water phase. So the amylose is partiallyleached out of the swollen starch granules. The branched amylopectineremains in the granules. The leaching process is limited by theavailable water. During cooling the amylose retrogrades very quickly andforms a gel. The retrogradation of amylopectine is believed to involveprimarily association of its outer branches and requires a longer timethan does the retrogradation of amylose, giving it prominence in thestaling process, which occurs over time after the product has cooled,aggregate more slowly, due to stereochemical interferences. Theamylopectine formed intramolecular bonds. The prominent role of starchin staling of bread is further illustrated by the use of carbohydrasesto diminish or to slow down the staling of baked products. It was shown(Conn J. F. et al. (1950) Cereal Chem., 27, 191-205) that amylases frombacterial or fungal origin slow down the rate of staling of bread andresult in a less firm crumb structure. The addition of thermostablealfa-amylases or beta-amylases is most effective. However this alsoresults in a gummy and sticky crumb.

The document EP0412607 discloses the use of a thermostablealfa-1,6-endoglucanase or an alfa-1,4-exoglucanase to reduce staling;EP0234858 discloses the use of a thermostable maltogenic beta-amylase toretain the crumb softness.

However, it is still not clear whether the anti-staling effect is due tothe dextrins produced or to the modification of the amylose andamylopectine and the consequent reduced tendency to crystallise. Alsothe influence of emulsifiers as glycerolmonostearate andsodiumstearoyllactylate seems to confirm the role of starch in breadcrumb firming (Schuster G. (1985) Emulgatoren für Lebensmittel—SpringerVerlag 323-329). It is the interaction between these emulsifiers and thestarch which results in a changed starch conformation that accounts forthe observed reduction of staling.

As there was not always a good correlation between starch structure andstaling (Zobel H. F. et al (1959) Cereal Chem., 36, 441), other flourconstituents were also investigated. The role of flour proteins in thecrumb firming process has been studied but it was found that they wereless important than starch (Cluskey, J. E. (1959) Cereal Chem., 36,236-246.), (Dragsdorf, R. D. et al. (1980) Cereal Chem., 57, 310-314)studied the water migration between starch and gluten during breadstorage. These authors concluded that due to a change in thecristallinity of the starch, it adsorbed more water, so the watermigrates from the gluten to the starch and so less free water isavailable.

In later study (Martin et al. (1991) Cereal Chem., 68(5), 498-503 and503-507), it appears that the high molecular weight dextrins do not havean antifirming effect on bread crumb. Instead, the high DP dextrins mayentangle and/or form a hydrogen bond with protein fibrils, thuseffectively cross-linking the gluten. Consequently, the firming rate isincreased. It is stated that in weaker flours the gluten interactsstronger with the starch granules. This results in bread crumb thatfirms faster. However better gluten quality and stronger flour alsoresult in higher loaf volume and thus in a softer crumb. Axford et al.(1968) cited in Faridi, H. (1985) Rheology of wheat products, AACC, p.263-264) showed that the loaf specific volume was a major factor inmeasuring both the rate and the extent of firming. So the role of glutenin bread firming remains still questionable and few attempts have beenmade to slow down firming based on gluten modification.

Proteases have a long history of use in the baking sector. They aremostly used by the baker to reduce mechanical dough developmentrequirements of unusually strong or tough gluten. They lower theviscosity and increase the extensibility of the dough. In the endproduct they improve the texture compressibility, the loaf volume andthe bread colour. Also the flavour can be enhanced by production ofcertain peptides. The proteases mellow the gluten enzymatically ratherthan mechanically. They reduce the consistency of the dough, decreasingthe farinograph value. The proteases most used in baking are fromAspergillus oryzae and Bacillus subtilis. The neutral bacterialproteases are by far more active on gluten than the alkaline proteases.Papain, bromelain and ficin are thiol-proteases extracted from papaya,pineapple and figs. Especially papain is very reactive towards glutenproteins. Bacterial proteases and papain, especially neutral proteases,are used in cookies, breadsticks and crackers where a pronouncedslackening of the dough is wanted. However, in breadmaking, a more mildhydrolysis of fungal proteases is preferred.

Proteases also have major disadvantages. The action of the proteases isnot limited in time, it continues after mixing and weakens the doughstructure in time. This phenomenon increases the risk of weakening thedough and increases the stickiness of the dough. Sometimes their actionis even enhanced by the pH drop during fermentation. The use ofproteases in baking requires strict control of the bulk fermentation andproofing conditions of the dough. The proteases are inactivated duringbaking (Kruger, J. E. (1987) Enzymes and their role in cereal technologyAACC 290-304). Especially neutral Bacillus proteases and papain shouldbe dosed very carefully as overdoses slacken the dough too much. Thismay result in dough collapse before ovening or a lower bread volume anda more open crumb structure. Especially in Europe, where the flours areweaker than in the US or Canada, the risk of overdosing protease is verypresent.

Furthermore, proteases also increase stickiness because by thehydrolytic action water is released from the gluten (Schwimmer, S.(1981) Source book of food enzymology-AVI Publishing, 583-584). Thismeans that in practice proteases are not much used in breadmaking inEurope.

The document EP021179 discloses the use of an alfa-amylase preparationin which the protease (inactivated) was used in combination withemulsifiers to inhibit staling.

Conforti et al. (1996) FSTA, 96(12), M0190 Abstract of presentation)added an enzyme mixture comprising bacterial amylase, fungal amylase andfungal protease to fat substituted muffins. The control fat containingmuffin was more tender. The enzyme treatment decreased the staling rate.This is not surprising in view of the presence of amylases.

Lipase is also known to soften bread crumb and to somewhat reduce thefirming rate of bread crumb (WO 94/04035 example 2).

Fungal proteases are sensitive to high temperatures. Their potency ofprotein hydrolysis in a moderate to high temperature range of about 50°C. or higher is normally poor. Some bacterial neutral and alkalineproteases are resistant to higher heat treatments. Till now reports onbacteria-derived proteases with heat resistance that can retain goodpeptidase activity, for example, in a high temperature range of about60° C. have been scarce. The document EP1186658 discloses such enzymeproduced by a bacterium of the genus Bacillus subtilis, morespecifically an M2-4 strain. The disclosed enzyme mixture, however,completely looses its activity at a temperature of about 70° C. Neutralthermostable proteases from Bacillus, which may be tolerant to oxidisingagents, are preferred in detergent formulations. Also alkalinethermostable proteases from Bacillus are used in washing and detergentformulations. Papain is very heat stable and requires a prolongedheating at 90-100° C. for deactivation. Bromelain is less stable and canbe deactivated at around 70° C. Other heat stable proteases are producedby Bacillus licheniformis NS70 (Chemical Abstracts, 127, 4144 CA),Bacillus licheniformis MIR (Chemical Abstracts, 116, 146805 CA),Bacillus stearothermophilus (Chemical Abstracts, 124, 224587 CA),Nocardiopsis (Chemical Abstracts, 114, 162444 CA) and Thermobacteroides(Chemical Abstracts, 116, 146805 CA). This is not an exhaustive list,but it illustrates the importance of the thermostable serine proteasesand their application, mostly in detergents. No reference is made tobaking and anti-staling properties.

Lipase is also known to soften bread crumb and to somewhat reduce thefirming rate of bread crumb (WO 94/04035 example 2).

Fungal proteases are sensitive to high temperatures. Some bacterialneutral and alkaline proteases are resistant to higher heat treatments.Neutral thermostable proteases from Bacillus, which may be tolerant tooxidising agents, are preferred in detergent formulations. Also alkalinethermostable proteases from Bacillus are used in washing and detergentformulations. Papain is very heat stable and requires a prolongedheating at 90-100° C. for deactivation. Bromelain is less stable and canbe deactivated at around 70° C. Other heat stable proteases are producedby Bacillus licheniformis NS70 (Chemical Abstracts, 127, 4144 CA),Bacillus licheniformis MIR (Chemical Abstracts, 116, 146805 CA),Bacillus stearothermophilus (Chemical Abstracts, 124, 224587 CA),Nocardiopsis (Chemical Abstracts, 114, 162444 CA) and Thermobacteroides(Chemical Abstracts, 116, 146805 CA). This is not an exhaustive list,but it illustrates the importance of the thermostable serine proteasesand their application, mostly in detergents. No reference is made tobaking and anti-staling properties.

Papain is a proteolytically active constituent in the latex of thetropical papaya fruit. The crude dried latex contains a mixture of atleast four cysteine proteinases.

Thermolysin is an extracellular, metalloendopeptidase secreted by thegram-positive thermophilic bacterium Bacillus thermoproteolyticus.

STATE OF THE ART

Keratinase is a protease which is active on keratin, a scleroproteinexisting as a constituent in mammalian epidermis, hair, wool, nails andfeathers. Practical applications of the enzyme are as ingredient indepilatory compositions; as dehairing aid of hides in leathermanufacture, the breaking down of keratin and reconstitution intotextile fabrics. No application of said enzyme in the food industry isknown.

Thermus aquaticus is a hyperthermophile belonging to the Archea. Thewell known “Taq polymerase”™ is isolated from this organism. Pyrococcusfuriosus is another representative from this group. Thermostableproteases were isolated from these organisms.

Thermitase is an extracellular endopeptidase from Thermoactinomycesvulgaris. Because of its relatively low cleaving specificity towardspeptide bonds, thermitase has many applications. It is suitable forproducing partially hydrolysed proteins for health and other specialdiets.

SUMMARY OF THE INVENTION

A first aspect of the present invention is related to a method for theprevention or retarding of staling and associated effects during thebaking process of bakery products, said method comprising the step ofadding a sufficiently effective amount of at least one thermostableprotease to the ingredients of said bakery products.

Preferably said proteases are neutral or alkaline proteases, mostpreferably alkaline proteases.

Preferably, the intermediate thermostable and/or thermostable serineprotease has its optimal temperature activity higher than 60° C.,preferably higher than 70° C., more preferably higher than 75° C. oreven higher than 80° C. The preferred intermediate thermostable and/orthermostable serine protease used in the method according to theinvention presents a ratio between the protease activity at optimumtemperature and the protease activity at 25° C., higher than 10,preferably higher than 15. As such the enzyme will preferably be activeduring the baking process and preferably not during the rising process.

Such intermediate thermostable and/or thermostable serine protease canbe obtained by extraction from naturally occurring eukaryotic orprokaryotic organisms, by synthesis or by genetic engineering by amethod well-known to a person skilled in the art.

The preferred intermediate thermostable and/or thermostable thermostableserine protease is Taq protease which can be advantageously isolatedfrom the strain Thermus aquaticus (LMG8924) or is keratinase, preferablyisolated from Bacillus licheniformis (LMG7561) or is thermitase isolatedfrom Thermoactinomyces vulgaris. These three proteinases all belong tothe class of the serine peptidases. Papain (belonging to the class ofcysteine peptidases) and thermolysin (belonging to the class ofmetallopeptidases) were also included in the baking trials performed butwere not able to reduce staling and/or had undesirable side effectsand/or negative effects on the baking process and the resultingproducts.

In the method according to the invention, use of the intermediatethermostable and/or thermostable serine protease can be combined withanother enzyme, such as a thermostable α-amylase, β-amylase,intermediate thermostable maltogenic amylase, lipase,glycolsyltransferases or pullulanases. The thermostable protease canalso be added to a non-enzymetic additive such as an emulsifier(monoglyceride, diglyceride and/or stearoyllactylades). Other suitableemulsifiers may also be added to said intermediate thermostable and/orthermostable serine protease during the baking process. Synergistic orcumulative effects are present.

Therefore, the method according to the invention will result in improvedbakery products which are preferably selected from the group consistingof bread, soft rolls, bagels, donuts, danish pastry, hamburger rolls,pizza, pita bread and cakes.

Another aspect of the present invention is related to an anti-stalingcomposition for bakery products comprising at least one thermostableprotease.

Another embodiment of the present invention is an improver composition,more specifically a bread improver composition, comprising at least oneintermediate thermostable and/or thermostable serine protease and theusual active ingredients of an improver composition. An improvercomposition is a well-known concept amongst bakers. It is a mixture ofactive ingredients such as enzymes and emulsifiers, which are mixed withthe usual ingredients for making bread, such as flour and water.

A further embodiment of the present invention is related to the use ofsaid intermediate thermostable and/or thermostable protease, especiallya keratinase of the invention in the food industry and more specificallyin bakery products.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to the use of an intermediate thermostable and/orthermostable serine protease in baked goods. Preferably, these serineproteases are alkaline proteases but they can also be neutral proteases.The enzyme preparation has a pronounced effect on crumb softness and onretarding the staling of baked products. The enzyme preparation ischaracterised by the fact that it has no adverse effect on doughrheology, on the crumb structure and on the volume of the resultingbread. The enzyme has a low activity at a temperature of 25° C. to 40°C. meaning that they will have no to low activity during dough restingand/or rising. The enzyme has a temperature optimum of 60° C.-80° C. orhigher. The enzyme is or is not inactivated during the baking process.The intermediate thermostable and/or thermostable serine proteasesaccording to the present invention are characterised by having apositive effect as anti-staling agents. This effect is especiallynoticeable in combination with other anti-staling enzymes. As examplesof other anti-staling enzymes the person skilled in the art may selectthermostable amylases from Bacillus licheniformis or Bacillusstearothermophilus and thermostable maltogenic amylases (i.e. Novamyl®from Novozymes). Their effect is also additive to the anti-stalingeffect of mono-en diglycerides, stearoyllactylates and other emulsifiersused in baking.

The intermediate thermostable and/or thermostable serine proteases ofthe invention can be used in bread, soft rolls, bagels, donuts, danishpastry, hamburger rolls, pizza and pita bread, cake and other bakedproducts where staling and inhibition thereof is an quality issue.

The intermediate thermostable and/or thermostable serine protease of theinvention can be produced by prokaryotes (bacteria) and eukaryotes(fungi, Archea, animals, plants etc) and/or can be produced by geneticengineering or even by synthesis with any technique known in the art.

Basically the most important characteristics of the proteases that areused in this invention are:

-   -   1) Their thermostability: At a pH where the enzyme is stable        they have a temperature optimum that is higher than 60° C.,        preferably higher than 70° C. and even more preferable higher        than 75° C., higher than 80° C. or 85° C.    -   2) The ratio between the activity at optimum temperature and at        25° C. is at least higher than 10 and preferable higher than 15.    -   3) They belong to the group of the serine proteases.

Preferably, the proteases of the invention do not lose their activity attemperatures higher than 60° C., preferably higher than 70° C., 75° C.,80° C. or even 85° C. The enzymes of the present invention may still beactive at the very high internal temperatures that are reached within aproduct during baking (at least about 75° C. for yeast leavened bakedfood and at least about 90° C.-95° C. for chemically leavened bakedfood, when fully baked). Within the optimum range of temperature, thetemperature may range anywhere from about 60° C. to 61° C., 62° C., 63°C., 84° C., 85° C., 89° C., 90° C., 94° C., 95° C. with all integersincluded therein.

The enzyme of the invention is preferably a keratinase, a Taq proteaseand/or a thermitase. The keratinase is preferably produced by Bacilluslicheniformis (example B. licheniformis LMG 7561). The Taq protease ispreferably produced by Thermus aquaticus (example Thermus aquaticus LMG8924). The thermitase is preferably produced by Thermoactinomycesvulgaris.

The proteases may be obtained from the respective micro-organisms by useof any suitable technique. For instance, the protease preparation may beobtained by fermentation of a micro-organism and subsequent isolation ofthe protease containing preparation from the resulting broth by methodsknown in the art such as centrifugation and ultrafiltration. Theproteases may also be obtained by cloning the DNA sequence coding for asuitable protease in a host organism, expressing the protease intra- orextra-cellular and collecting the produced enzyme. Preferably, theprotease is present in a form that allows exact and/or more or lessexact dosing. Dosing can be difficult when the proteases are part of acomplex natural mixture comprising more than one type of enzymes. Insuch case, the enclosure of one or more purification steps might beneeded.

The proteases may also be obtained by directed evolution or geneshuffling of thermostable or non-thermostable serine proteases orenzymes. As long as they have peptide cleaving activity, they areconsidered to be proteases in the scope of this invention.

Surprisingly, the inventors found that the use of a protease which hadno perceivable action on the dough rheology had a pronounced effect onthe softness and retardation of the crumb hardness. There was no adverseeffect on the crumb elasticity or no increase of the crumb stickiness ascompared to a control. The effect was additive to known anti-stalingagents (such as α-amylases) and permits the development of bread andother soft bakery products with a prolonged shelf life.

The choice of the protease is very important. The protease should exertno adverse effect during mixing and the subsequent proofing. Otherwisethe dosage that can be administered is to low to diminish the stalingrate and to maintain a good crumb elasticity. The higher the temperatureoptimum of the enzyme, the lower the negative effect on the crumbstructure and on the dough rheology.

The present invention will be described hereafter in detail in thefollowing non-limiting examples and in reference to the enclosedfigures.

DESCRIPTION OF THE FIGURES

FIG. 1 represents the protease temperature optimum expressed in functionof the relative activity (%) at pH 7.0, in a buffered solution of 0.1 Mphosphate for aqualysin I (♦, full line) and keratinase (, dottedline).

FIG. 2 represents the retarding effect of the addition of Taq protease(0 U: ♦, 800 U: ▴) upon staling of bread in the absence and presence ofNovamyl® (0-8 g/100 kg flour).

FIG. 3 shows the improved effect on retarding bread staling followingthe addition of keratinase (0 U: ♦, 800 U: ▪) in bread in the absence orpresence of Novamyl® (0-8 g/100 kg flour).

FIG. 4 shows the temperature optimum of thermitase, expressed infunction of its relative activity (%) at pH 7.0, in a buffered solutionof 0.1 M phosphate.

FIG. 5 shows the thermal stability of thermitase, expressed in functionof its relative activity (%).

DESCRIPTION OF THE PREFERRED EMBODIMENT

One of the preferred serine proteases used, is obtained from the strainBacillus licheniformis LMG 7561 and has keratinase activity. By aminoacid similarity and phenylmethylsulfonyl fluoride inhibition, thekeratinase was demonstrated to be a serine protease. The keratinase inquestion is obtained by culturing the strain Bacillus licheniformis LMG7561 on the following medium: 0.5 g/l NH₄Cl, 0.5 g/l NaCl, 0.3 g/lK₂HPO₄, 0.4 g/l KH₂PO₄, 0.1 g/l MgCl₂.6H₂O, 2 g/l citric acid, 0.1 g/lyeast extract and 10 g/l feather meal. The medium is adjusted to pH 6.5with phosphoric acid. No pH control is imposed. Incubation is done at45° C. with aeration (p₂ 60%, 1.25 vvm) during 40 hours after which themedium is collected for further concentration. The supernatant is thenconcentrated by membrane ultrafiltration (molecular cut off: 5,000 Da).The crude keratinase solution obtained that way is stored frozen untilused in baking tests.

The keratinase solution obtained that way displays maximum activity at atemperature of 60° C. and a pH of 8.0. In the pH range of 7 to 9 morethan 85% of the maximum activity was measured. There isn't almost anyloss of enzyme activity while heating the solution an hour at 60° C.Heating the enzyme at 70° C. during 14 min reduces the activity with50%.

The activity was measured on keratin. For standard measurements, 4 g ofkeratin were dissolved in 100 ml sodium hydroxide. After dissolution thepH is adjusted slowly to 8.0 with 3.2 M phosphoric acid. Distilled wateris added to a final volume of 200 ml. 5 ml of the substrate solution ispre-incubated at 60° C. 1 ml of enzyme solution is added and incubatedat 60° C. Then 5 ml of 14% TCA (TriChloroAcetic acid) is added to theincubated enzyme solution. Mixed for 60 minutes. The solution isfiltered and the absorbance is measured at 275 nm relative to a blanksolution (enzyme added after the TCA addition).

The activity is expressed as

${{KU}\text{/}m\; l} = \frac{\left( {{A\; 275\mspace{14mu} {nm}\mspace{14mu} {Enzyme}} - {A\; 275\mspace{14mu} {nm}\mspace{14mu} {Blanc}}} \right)*11}{0.0075*30}$

The fermentation contained 300 to 1500 KU/ml.

For baking purposes the activity was expressed as mU/ml based on theprotazym tablet determination. The KU were only used to demonstrate thepresence of the keratinase.

The Taq protease in question is obtained by culturing the strain Thermusaquaticus LMG 8924 on the following medium: 1 g/l tryptone; 1 g/l yeastextract; 100 ml/l salt solution and 900 ml distilled water. The pH isadjusted to 8.2 with 1 M NaOH prior to sterilisation 121° C. for 15minutes. The salt solution has the following composition: 1 g/lnitriloacetic acid 0.6 g/l CaSO₄.2H₂O; 1 g/l MgSO₄.7H₂O; 80 mg/l NaCl,1.03 g/l KNO₃; 6.89 g/l NaNO₃; 2.8 g/l Na₂HPO₄.12H₂O; 10 ml/l FeCl₃.6H₂Osolution (47 mg/100 ml); 10 ml/l Trace element solution and 1 ldistilled water. The Trace element solution has the followingcomposition: 0.5 ml/l H₂SO₄; 1.7 g/l MnSO₄.H₂O; 0.5 g/l ZnSO₄.7H₂O; 0.5g/l H₃BO₃; 25 mg/l CuSO₄.5H₂O; 25 mg/l Na₂MoO₄.2H₂O; 46 mg/l CoCl₂. 6H₂Oand 1 l distilled water. Incubation is done at 60° C. with aeration (p0₂60%, 4 vvm) during hours after which the medium is collected for furtherconcentration. Thermus aquaticus LMG 8924 produced at least two kinds ofextracellular proteases. One of the extracellular proteases was calledaqualysin I, and is an alkaline protease which was secreted linearlyfrom the early stationary phase until the time the cells ceased to grow.The optimum temperature of the proteolytic activity was between 70 and80° C. The other was called aqualysin II and is a neutral protease, theproduction of which appeared from day 4 and the concentration of thisprotease continued linearly for 5 days. The maximum activity wasobtained at 95° C. (the highest temperature tested). The fermentationextract was used after 1 day of fermentation for the baking tests. Asthe fermentation was stopped after 1 day, the protease present is theaqualysin I. Aqualysin I is strongly inhibited by the microbial serineprotease inhibitors and can be classified as an alkaline serineprotease.

The supernatant is then concentrated by membrane ultrafiltration(molecular cut off: 10,000 Da). The crude Taq protease solution obtainedthat way is stored frozen until used in baking tests.

The Taq protease solution obtained that way displays maximum activity ata temperature of 80° C. There isn't almost any loss of enzyme activitywhile heating the solution an hour at 80° C. Heating the enzyme at 90°C. during 10 min reduces the activity with 60%.

The protease activity was measured on azurine-crosslinked casein(AZCL-casein). It is prepared by dyeing and crosslinking casein toproduce a material which hydrates in water but is water insoluble.Hydrolysis by proteases produces water soluble dyed fragments, and therate of release of these (increase in absorbance at 590 nm) can berelated directly to enzyme activity (Protazyme AK Tablets, Megazyme,Ireland). A protazyme AK tablet is incubated in 100 mM Na₂HPO₄.2H₂O; pH7.0 at 60° C. for 5 min. An aliquot of enzyme (1.0 ml) is added and thereaction is allowed to continue for exactly 10 min. The reaction isterminated by the addition of tri-sodium phosphate (10 ml, 2% w/v, pH12.3). The tube is allowed to stand for approx. 2 min at roomtemperature and the contents are filtered. The absorbance of thefiltrate is measured at 590 nm against a substrate blank.

The activity is expressed as

mU/ml=(34.2*(Abs₅₉₀enzyme−Abs₅₉₀blank)+0.6)/dilution

In the case of the thermophilic microorganism, Thermoactinomycesvulgaris, it is known that during the logarithmic phase ofmultiplication several proteolytic enzymes are secreted into thesurrounding medium. Among the up to five proteolytic components of theculture filtrate one protease dominates amounting 70 to 80% of the totalactivity, termed thermitase.

Thermitase is an extracellular, thermostable serine proteinase. The pHprofile shows a broad optimum between pH 7.5 and 9.5. The enzymedemonstrates maximal stability in the pH range of 6.4 to 7.6 withincreasing instability beyond pH 8.0 and below 5.75, especially atelevated temperatures and longer time periods. Depending on the size ofthe substrate, thermitase shows maximum activity at temperatures rangingfrom 65° C. (gelatin), 70° C. (protamine) to 85° C. (azocasein). Thetemperature optimum is most pronounced with the biggest substrate(azocasein): activity at 85° C. is 12 times over the activity shown at25° C.

Thermitase in question is obtained by culturing the strainThermoactinomyces vulgaris NRRL b-1617 in a culture medium with thefollowing composition: wheat starch (20 g/l), bacteriological pepton (5g/l), yeast extract (3 g/l) and malt extract (3 g/l) in destilled water.Incubation is done at 45° C. with an aeration of 12 l/min and a rotationof 200 rpm. The supernatant was collected after 24 h of incubation.Because of the fact that the culture supernatant contained a lot ofα-amylase activity, a first purification step was performed to separatethe protease activity from the α-amylase activity to perform bakingtrials. The supernatant was concentrated by membrane ultrafiltration(molecular cut off: 10,000 Da). Thermitase was purified by columnchromatography on a S-sepharose column (Pharmacia). The column wasequilibrated with 500 mM Na-acetate buffer (pH 4.5) and afterwards with10 mM Na-acetate buffer (pH 4.5) and 5 mM CaCl₂. The α-amylase activitydidn't bind on the column and thermitase was eluted with 10 mMNa-acetate buffer (pH 4.5), 5 mM CaCl₂ and 1 M NaCl. The eluted fractionwas dialysed against 10 mM Na-acetate buffer (pH 4.5) and 5 mM CaCl₂ andused to perform baking trials.

Side-activities like α-amylase activity was measured by the PhadebasAmylase Test™ (Pharmacia & Upjohn). The substrate is a water-insolublecross-linked starch polymer carrying a blue dye. It is hydrolysed byα-amylase to form water-soluble blue fragments. The absorbance of theblue solution is a function of the α-amylase activity in the sample.

Xylanase side-activity was measured by the Xylazyme Method™ (Megazyme).The substrate employed is azurine-crosslinked xylan. This substrate isprepared by dyeing and crosslinking highly purified xylan (frombirchwood) to produce a material which hydrates in water but is waterinsoluble. Hydrolysis by endo-(1,4)-β-D-xylanase produces water solubledyed fragments, and the rate of release of these (increase in absorbanceat 590 nm) can be related directly to enzyme activity.

The Taq protease solution obtained didn't show any α-amylase or xylanaseside activity.

The keratinase solution obtained had no xylanase activity and containedless than 8 U/ml α-amylase activity as measured by Phadebas test.

The thermitase solution obtained after the purification process didn'tshow any α-amylase or xylanase side activity.

The baking tests were performed in 1 kg bread. The basic recipe was (ingrams):

Flour (Duo): 1500 Water: 840 Fresh Yeast (Bruggeman, Belgium): 75 SodiumChloride: 30 Partially hydrogenated palm oil: 21 Distilledmonoglycerides: 3 Saccharose: 6 Ascorbic acid: 0.06

The following breadmaking process was used: The ingredients were mixedfor 2′ at low and 6′ at high speed in a Diosna SP24 mixer. The finaldough temperature was 29° C. After bulk fermentation for 20′ at 25° C.,600 g dough pieces were made up using the Euro 200S (Bertrand-ElectroluxBaking) set at R8/L19 and moulded. The dough pieces are proofed at 35°C. for 50′ at 95% relative humidity. Then the breads are baked at 230°C. in a MIWE CONDO (Micheal Wenz-Arnstein-Germany) oven with steam (0.1L before and 0.2 L after ovening the breads). It is obvious to oneskilled in the art that same end results can be obtained by usingequipment of other suppliers.

The softness of the bread was measured by a TA-XT2 texture analyser(Stable Micro Systems UK). The bread was sliced and the force to obtaina 25% deformation of 4 slices of lcm was measured. This is called thehardness. The hardness is measured at day 1 and day 6 after baking. Thedifference between the two measure forces is “the loss of softness”:

Loss of softness=deformation force at

day 6-deformation force at day 1

It is a relative measure. The absolute values have no meaning as suchbut should be compared to a reference for interpretation.

The elasticity is the difference between the aforementioned force andthe force after 20 sec of relaxation. When the elasticity is lower thanin the reference bread, this means that the crumb becomes lessresilient. The crumb, when compressed does not regain its originalshape. This means that during slicing or handling the crumb structuremay be lost irreversibly. It is important that by using an added enzymethere is no loss of elasticity compared to a control bread.

Addition of the enzymes of the present invention to the bread dough didnot change the proof time, loaf moisture and specific load volume. Theinitial moisture content of bread varied slightly, but all the loaveslost approximately the same amount of moisture during six days ofstorage at room temperature.

EXAMPLES Example 1 Taq Protease

A bread has been baked according to the aforementioned method withaddition of Taq protease (eventually in the presence of different dosesof Novamyl® 10 000 BG from Novozymes (Denmark)).

Doses are expressed on 100 kg of flour weight used in the baking test.

The following Table 1 expresses the loss in softness between day 1 andday 6 after baking as defined previously.

TABLE 1 Softness Novamyl ® g/100 kg 800 U Taq protease 0 U Taq protease0 140 209 2.5 128 152 5 96 118 8 68 105

The example shows that the use of Taq protease will retard staling inbread. A combination of Taq protease with an intermediate thermostablemaltogenic amylase (e.g. Novamyl®, commercial enzyme of Novozymes) willretard staling in bread significantly. So there is a synergistic effectbetween the thermostable serine proteases and α-amylases. This effectbecomes more pronounced at higher doses of Novamyl® (see FIG. 2).

Table 2 shows that the elasticity of the bread crumb is hardly affectedby the use of the Taq protease.

TABLE 2 Elasticity Novamyl ® 800 U Taq g/100 kg protease 0 U Taqprotease 0 61.5 61.9 2.5 63.1 63.4 5 63.0 64.2 8 63.4 64.9

Example 2 Keratinase

A bread baked according to the aforementioned method with the additionof keratinase (eventually in the presence of Novamyl® 10 000 BG fromNovozymes (Denmark)).

Doses in the following Table 3 are expressed on 100 kg of flour weightused in the baking test.

Table 3 expresses the loss in softness between day 1 and day 6 afterbaking as defined previously.

TABLE 3 Softness Novamyl ® g/100 kg 800 U keratinase 0 U keratinase 0121 209 2.5 95 126 5 64 111 8 50 59

It is clear from this experiment that adding the thermostable serineprotease keratinase has a pronounced effect on softness. There is acumulative effect with thermostable maltogenic amylases as Novamyl® (seeFIG. 3). It was verified that the small quantity of amylase present inthe preparation had no impact on softness and the relaxation ratio bytesting this amylase separately.

Table 4 also shows that there is no adverse effect on the relaxationratio when this protease is used.

TABLE 4 Elasticity Novamyl ® g/100 kg 800 U keratinase 0 U keratinase 062.6 63.6 2.5 64.3 65.0 5 65.5 65.8 8 65.4 65.8

Example 3 Thermitase

A bread baked according to the aforementioned method with the additionof thermitase (eventually in combination with Novamyl® 10 000 BG fromNovozymes (Denmark)).

Doses in the following Table 5 are expressed on 100 kg flour weight usedin the baking test.

Table 5 expresses the loss in softness between day 1 and day 6 afterbaking as defined previously.

TABLE 5 Softness Novamyl ® 10.500 U g/100 kg Thermitase 0 U Thermitase 0140 197 2.5 87 107 5 65 102 8 62 68

It is obvious from this experiment that adding the thermostable serineprotease thermitase has a pronounced effect on softness. There is also acumulative effect with thermostable maltogenic amylases as Novamyl®.After purification of thermitase there was no alfa-amylase present inthe preparation that could have an impact on softness and the relaxationratio.

Table 6 shows that there is also no adverse effect on the relaxationratio when this protease is used.

TABLE 6 Elasticity Novamyl ® 10500 U 0 U g/100 kg Thermitase Thermitase0 62 64 2.5 64 65 5 64.6 66.3 8 64.4 66.2

The thermitase optimum relative activity (%) of protease at pH 7.0, in abuffered solution of 0.1 M phosphate and the thermal stability(expressed in function or the relative stability at a given temperature)are given in FIGS. 4 and 5 respectively.

Treatment with Taq protease, keratinase and/or or thermitase alone, asmixture and/or together with thermostable amylases (e.g. Novamyl®)significantly affects bread softness. The enzyme treated bread wassofter, when Taq protease, keratinase and/or thermitase were added. Theexamples illustrate that thermostable serine proteases according to thepresent invention increase shelf live of baked products as far assoftness and staling are concerned.

Example 4 Effect of Keratinase, Thermitase and Taq Protease on the CrumbStructure and the Sensory Characteristics of Bread

The above-mentioned intermediate thermostable and/or thermostable serineproteases according to the present invention did not have a negativeeffect on the crumb structure, whereas other non-thermostable proteasesor proteases belonging to another group of proteases like papain(cysteine peptidase) or thermolysin (metallopeptidase) did. Use of forinstance papain or thermolysin resulted in the crumb structure becomingmore open, dependent of the doses that were used. There was also noeffect on the volume of the baked products by using the thermostableserine proteases of the invention.

Crust colour, character of crust, colour of crumb, aroma and taste ofbread did not change significantly with the addition of keratinase, Taqprotease and/or thermitase.

Example 5 Application of Taq Protease in Cake

Recipe: Mix Satin Crème Cake: 1000 g

Eggs: 350 g

Oil: 300 g

Water: 225 g

Method: Mixer: Hobart

Instrument: Padle

Speed: 1 min speed 1 and 2 min speed 2 than

Adding oil and water, 1 min speedl, scrape

Down and 2 min speed 1

Batter weight: 300 g

Temperature: 180° C.

Time: 45 min

Doses in the following Table 7 are expressed on 100 kg of flour weightused in the baking test.

Table 7 expresses the loss in softness measured after 4 days, 1 week, 2weeks and 3 weeks after baking.

TABLE 7 Softness 0 U Taq 600 U Taq 1200 U Taq protease protease protease4 days 396 321 237 1 week 492 379 298 2 weeks 542 457 268 4 weeks 687441 308

What is claimed is:
 1. An improver composition for the prevention orretarding of staling during the baking process of bakery productscomprising at least one intermediate thermostable or thermostable serineprotease having a temperature activity optimum between 60° C. and 95°C.; wherein the ratio between the protease activity in said improvercomposition at optimum temperature and the protease activity at 25° C.is higher than
 10. 2. The improver composition according to claim 1,wherein the protease has a temperature activity optimum higher than 70°C.
 3. The improver composition according to claim 1, wherein the ratiobetween the protease activity at optimum temperature and the proteaseactivity at 25° C. is higher than
 15. 4. The improver compositionaccording to claim 1, wherein said protease is obtained by extractionfrom naturally occurring eukaryotic or prokaryotic organisms, bysynthesis or by genetic engineering
 5. The improver compositionaccording to claim 1, wherein said protease is a Taq protease, akeratinase and/or a thermitase.
 6. The improver composition according toclaim 1, wherein said protease is selected from the group consisting ofaqualysin I, aqualysin II, keratinase and thermitase.
 7. The improvercomposition according to claim 1, wherein the thermostable serineprotease is a Taq protease isolated from Thermus aquaticus LMG 8924, akeratinase isolated from Bacillus licheniformis LMG 7561 and/or athermitase isolated from Thermoactinomyces vulgaris.
 8. The improvercomposition according to claim 1 further comprising an anti-stalingadditive selected from the group consisting of thermostable α-amylase,β-amylase, intermediate thermostable maltogenic amylase, lipase,glycolsyltransferases, pullulanases and emulsifiers.
 9. The improvercomposition according to claim 8, wherein said intermediate thermostableor thermostable serine protease is a Taq protease and said anti-stalingadditive is an intermediate thermostable maltogenic amylase.
 10. Theimprover composition according to claim 1, wherein said improver is abread improver.